1. Any widespread contagious disease associated with a high death rate. 2. An often fatal disease caused by Yersinia pestis. The natural hosts are ground squirrels, wild rodents, and rats; the vector is the rat flea. In the U.S., hunters, trappers, and campers may encounter infected mammals. Outbreaks are also associated with crowded living conditions and poor sanitation. Although plague was responsible for millions of deaths during the Middle Ages, improvements in sanitation, medical care, and the availability of antibiotics now prevent widespread epidemics. Plague is characterized by high fever, restlessness, confusion, prostration, delirium, shock, and coma. Streptomycin (the antibiotic of choice), gentamicin, tetracyclines, doxycycline, fluoroquinolones, and chloramphenicol are effective in treating plague. In the U.S., about 15 cases of plague are reported annually , primarily in western and southwestern regions. If treated promptly, plague is rarely fatal; however, in the U.S. about 1 in 7 people infected dies, usually because of delayed diagnosis or treatment.